1. Field of Invention
This invention pertains generally to photometric analyzers and, more particularly, to a photometric detector assembly with automated calibration filters for use in a photometric analyzer such as an inline optical sensor.
2. Related Art
U.S. Pat. No. 5,905,271 discloses an inline optical sensor which can be utilized in a wide variety of applications (e.g. spectrophotometers, colorimeters, turbidimeters, refractometers, and ultrasonic flow and particle sensing devices) for monitoring photometric the properties of a fluid product stream. Such instruments generally have a light source and a detector positioned on opposite sides of the product stream, with the light source directing a beam of light through the product stream to the detector. The light can be in the ultra violet, visible or near infrared spectrums, and the term light is used herein as including all three.
When inline photometric analyzers are used as a primary measurement source for controlling critical filtration and separation processes, particularly in the biotech and pharmaceutical fields, NIST traceable calibration standards must generally be used in order to comply with validation protocols and procedures. Such standards are typically in the form of filters which are placed between the light source and detector. These filters are subject to deterioration with use and exposure to the environment, and they must be re-certified periodically.
U.S. Pat. No. 6,512,223 discloses a photometric detector assembly which includes a pair of NIST traceable calibration filters enclosed within a sealed housing and means outside the housing for manually moving the filters into and out of the path of a beam between calibration and normal operating positions. This system can be calibrated to a high degree of accuracy, and being in sealed housing and exposed to the beam only on a limited basis, the filters do not need to be cleaned and/or replaced as often as they otherwise would. However, it movement the filters between the calibration and operating positions is a manual operation.